Barking drums of the general type noted above are known, as shown for example in Canadian Patent 813,131. Pulpwood logs (roundwood) introduced into the barking drum are tumbled around during simultaneous travel in the length direction of the drum, during which they are freed from bark by friction against each other and, to a certain extent, against the drum wall. In the embodiment shown in the above-noted Canadian patent, the drum itself is cylindrical, which is most common nowadays, although many other shapes have been suggested both prior to said patent and subsequently. In Swedish Pat. No. 27,096, for example, the drum is of slightly conical shape, such that it is somewhat larger at the discharge end than at the inlet end, whereby the wood can be conveyed through the drum automatically without the need for the drum to be inclined. In contrast to this arrangement, FIG. 6 of U.S. Pat. No. 1,300,536 shows how a cylindrical drum has been provided with a series of retarding devices in the form of transverse partitions arranged at a distance from each other along the axis of the drum and having central openings of gradually decreasing diameters towards the discharge end of the drum to permit the wood to pass therethrough.
Further, it has been suggested in U.S. Pat. No. 1,700,390 that a cylindrical drum be provided with a special infeed section consisting of a truncated cone, smooth on the inside and with a small inlet diameter and a large discharge diameter. Full scale trials have proven that this suggestion is not feasible. Another proposal that is intended to increase the degree of filling of the drum is shown in FIGS. 3 and 4 of Swedish Pat. No. 75,658. Here the drum is divided up into separately supported and separately driven sections of different diameters. The sections nearest the drum ends have larger diameters than the sections nearest the middle of the drum, and these sections of larger diameter are arranged with their axes of rotation at the side of and above the axes of rotation of the middle sections in such a way that the degree of filling of the middle sections can be increased.
A barking drum is described in Soviet Union Pat. No. 479,624 in which the shell of the drum is constructed as a truncated cone with log lifters attached to the inside. The discharge half of the drum is narrower and is provided with bark discharge slots, while the inlet half is wider, has no bark discharge slots, and is fitted with an annular flange extending inwards at the inlet end, whereby a quantity of water can be retained in the inlet half for soaking the wood. A barking drum constructed in this way is stated to be of simplified design and to have an increased capacity.
The use of different numbers of log lifters in separate sections of the drum is also known in a barking drum, as disclosed for example in German Auslegeschrift No. 1 202 470. In this a cylindrical barking drum is described with bark discharge slots at the discharge end only. The inside of the drum is divided axially into chambers by means of annular partitions, and the inside diameter of the annular partitions increases from the inlet end to its discharge end. The drum consists of two halves, an inlet half and a discharge half, which are separately supported in bearings and separately driven, and in the discharge half there is a larger number of log lifters than in the inlet half, for reasons not stated.
In all cases, the known barking drums are intended and designed for barking pulpwood logs, specifically, logs which have previously been removed of limbs in preparation for barking, and are not intended for processing logs having limbs, such as the trimmings from the pulpwood logs or smaller trees removed in thinning.